First-Order Superconducting Phase Transition inCeCoIn5

Abstract

The superconducting phase transition in heavy fermion CeCoIn5 (T(c)=2.3 K in zero field) becomes first order when the magnetic field H parallel [001] is greater than 4.7 T, and the transition temperature is below T0 approximately 0.31T(c). The change from second order at lower fields is reflected in strong sharpening of both specific heat and thermal expansion anomalies associated with the phase transition, a strong magnetocaloric effect, and a steplike change in the sample volume. This effect is due to Pauli limiting in a type-II superconductor, and was predicted theoretically in the mid-1960s.

Multiple phase transitions in Pauli-limited iron-based superconductors

“…The latter is the temperature T + , in which phase transitions from the superconducting to normal state change kind, from first to second order. T C is reported as 2.3 K and 3.5 K for CeCoIn 5 and KFe 2 As 2 respectively, while in both cases T + can be approximated as 0.31 T C [8,19]. In CeCoIn 5 the specific heat displays an additional anomaly within the superconducting state at a temperature ∼ 300 mK (∼ 0.12 T C ) [7].…”

“…in multiband superconductors like IBSC [33][34][35][36] or MgB 2 [37,38]. Specific heat measurements have been also successfully used to investigate the FFLO phase in heavy-fermion systems [7,8,11] and organic superconductors [14], where the peaks, deep in the superconducting state in the LTHM regime, have been interpreted as phase transitions from BCS to FFLO state.…”

“…Only in the last decade systems have appeared in which we expect an experimental verification of this phase, such as heavy-fermion superconductors [6] (e.g. CeCoIn 5 [7][8][9][10][11]) or organic superconductors (e.g. [14][15][16][17][18]).…”

Field-Induced Quantum Critical Point and Nodal Superconductivity in the Heavy-Fermion SuperconductorCe2PdIn8

“…While there is no static magnetism in CeCoIn 5 at zero field, a field-induced antiferromagnetic (AF) quantum critical point (QCP) has been clearly demonstrated by resistivity and specific heat measurements [7,8]. Initially, it was very puzzling why the AF QCP is located right at the upper critical field H c2 .Meanwhile, the observations of first-order phase transition at low temperature and H c2 and a second magnetization and specific heat anomaly well inside the superconducting state have been interpreted as the signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state [5,[9][10][11][12]. The novel FFLO state with broken spatial symmetry was predicted in the 1960s [13,14], but it has never been experimentally verified before.…”

“…Meanwhile, the observations of first-order phase transition at low temperature and H c2 and a second magnetization and specific heat anomaly well inside the superconducting state have been interpreted as the signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state [5,[9][10][11][12]. The novel FFLO state with broken spatial symmetry was predicted in the 1960s [13,14], but it has never been experimentally verified before.…”